THROWIN’ STRONG: Kevin Youkilis throws out Robinson Cano from third base during the sixth inning of the Yankees’ 5-4 loss to the Red Sox last night. AP

A scary thought for Yankees fans as their team lost 5-4 to the Red Sox on Friday the 13th: Maybe your club’s best chance to separate in the AL East has come and gone.

Because are the Yankees really going to have more favorable conditions than they have experienced over the first six weeks this season? Consider:

* The Red Sox have played as badly as seems possible, yet are now just three games behind the second-place Yankees.

* The Rivalry opener was the Yankees’ 22nd home game this year, more than any team except Kansas City.

* They have yet to have to travel to the West Coast.

* Three rainouts have given an older team plenty of off-days.

* The rotation has not been the albatross expected and, in fact, has been something closer to a strength.

Now think about these issues for the rest of the season. The Red Sox’s best play is almost certainly in front of them. The onerous aspects of the Yankee road schedule are coming, including both West Coast trips. Plus, the Yankees now have to make up those three postponements, which will mean fewer offdays and greater stress on that older roster.

And are you a believer in this rotation? Because it is still a while until the Yankees can pluck a starter in the trade market, if somebody worthwhile actually is even available.

Now maybe Rafael Soriano gets his act together or Phil Hughes gets healthy and effective, or Derek Jeter and Jorge Posada reach back to a better time and that revs the Yanks into a strong, sustained run.

But, for now, it feels as if the Yankees have failed to maximize a time when they had a favorable schedule, reasonably good health and the Red Sox were performing in a substandard way.

The Yanks’ play had been disturbing enough recently — sloppy on defense, not opportunistic on offense — that manager Joe Girardi called a meeting last night of the whole team, including coaches, to stress the need to clean up the play.

“We have not played very well for the last week and half to two weeks,” Girardi said.

The problems persisted last night. Even after Girardi’s powwow. Even with The Rivalry renewed, a factor Girardi had hoped would jolt his club. Even with the new Stadium filled (48,254) and as loud and into a game as it had been perhaps all season.

The Yankees permitted an unearned run in the fourth via a Russell Martin passed ball. The failure to complete a makeable double play in the seventh — Robinson Cano never threw to first after taking a feed from Jeter — contributed to three Boston runs that broke a 2-2 tie.

Meanwhile, on offense the Yankees were just 2-for-14 with men on base. The Yankees over the years have made their reputation by doing damage when working into favorable counts. But against Red Sox starter Clay Buchholz and reliever Daniel Bard the Yanks generated 13 hitter’s counts — 2-0, 3-0 or 3-1 — and went 1-for-11 with two walks, three strikeouts and not a single ball driven into the outfield in those situations besides Posada’s ground single that preceded Martin’s homer in the fifth.

Is it possible that the offense that was supposed to carry the Yankees is what you see: Hit or miss, homer dependent, loaded with dead spots.

The bigger question, though, might be about regret. Suddenly, Carl Crawford and, especially, Adrian Gonzalez (homer and two RBIs last night) are hitting, which augurs well for Boston being what was expected: the AL East favorite.

The Yanks are now two games behind Tampa Bay, watching the Red Sox creep up in the rearview mirror. The schedule will not be as favorable the rest of the way; and can the Yankees really expect A.J. Burnett, Freddy Garcia and Bartolo Colon (who pitched well last night) to maintain over the final 20 weeks what they have positively offered in the first six?

Have the Yankees already fumbled their best chance to control the AL East?